Research Project: Production and Disease and Pest Management of Horticultural Crops

Location: Southern Horticultural Research

2016 Annual Report

Objectives
Objective 1: Develop integrated strategies to control invasive diseases and pests within the context of small fruit production systems of the Gulf Coast. Sub-objectives: 1.1: Determine the importance of wild fruit hosts to the ecology and life history traits of Spotted-wing Drosophila (SWD) and other vinegar fly pests of fruit crops of the U.S. Gulf Coast, with an emphasis on fly population dynamics in surrounding landscapes. 1.2: Develop and evaluate Integrated Pest Management (IPM) strategies involving selective chemical application. 1.3: Determine pathogen lifecycle events and spread patterns of bacterial leaf scorch, a new and emerging disease of blueberries in the Gulf South. 1.4: Develop disease screening assays using traditional and molecular screening techniques to identify disease resistant small fruit germplasm and characterize relevant host/pathogen relationships, the influence of cultural practices, and virulence levels of pathogens. 1.5: Develop disease control protocols based on cultural practices of removing rosette infected primocanes, which are a source of fungal inoculum, to reduce rosette disease severity in erect blackberry cultivars. Objective 2: Develop disease and pest control strategies that can be readily integrated with existing production practices used in container-grown ornamental plant nursery systems. Sub-objectives: 2.1: Develop a three-step ‘push-pull’ management strategy for protecting vulnerable nursery tree stock from ambrosia beetles. 2.2: Examine the effect of binding and leaching potential of soil-incorporated insecticides in alternative and standard soilless substrates in container-grown ornamental plants. 2.3: Determine optimal timing of disinfestant to restrict pathogen dispersal through irrigation water and limit plant disease. 2.4: Develop a comprehensive preventive and reactive disease management strategy to control Pseudomonas, Colletotrichum, and Rhizoctonia in plant propagation facilities. 2.5: Develop an integrated disease management strategy to control Leyland cypress blight in ornamental plant nursery production. 2.6: Identify changes in spray patterns across 100 foot blocks of container-grown plants using commercial sprayer equipment that correlate with reduction in disease intensity. Objective 3: Develop and improve pollination practices on berry and vegetable farms along the Gulf Coast and increase capability to use native bees.

Approach
Develop an updated pest management program to control the spotted-wing Drosophila fly from damaging fruits and vegetables. Develop cultural and chemical controls and tolerant cultivars of several small fruit diseases, with emphasis on Phytophthora root rot, a serious existing disease, and Xylella bacterial leaf scorch, a new disease of blueberry. Identify habitat sources of ambrosia beetle, and characterize repellant and attractant strategies that prevent ambrosia beetle movement into ornamental plant nurseries. Develop updated plant disease management practices to control existing and new pathogens in propagation, to time disinfestant treatments that prevent spread of Phytophthora in irrigation water, and to produce a risk-based fungicide timing model to control Passalora blight of Leyland cypress in the nursery. Nesting habitat for native pollinators will be promoted to expand bee management practices that are critical for achieving profitable fruit and vegetable yields.

Progress Report
In 2016, a small fruit entomology group determined environmental stress in spotted wing drosophila (SWD) flies was associated with the physical characteristics of host fruits. ARS researchers from Poplarville and Corvallis began screening Vaccinium fruit from around the World for possible resistance or tolerance to SWD infestation. Additionally, Poplarville researchers working with geneticists at the University of Southern Mississippi, used molecular techniques (next-generation 454 pyrosequencing) to identify symbiotic or pathogenic bacteria carried internally within male and female SWD flies, some of which might be exploited for genetic control of this global fly pest. In 2016, a small fruit pathologist determined pathogen lifecycle events and spread patterns of bacterial leaf scorch, a new and emerging disease of blueberries in the Gulf South. Bimonthly sampling determined that the pathogen, X. fastidiosa, was detected most consistently in root sap and least consistently from single-stem sap by real-time PCR, and most reliably in summer and least reliably in April from leaf petiole/midrib tissues or current year's shoot growth tissues by ELISA. Traditional and molecular disease screening assays were used to characterize host-pathogen relationships, virulence levels of pathogens, and the influence of cultural practices; and to identify disease resistant small fruit germplasm. Four greenhouse studies were done to investigate effects of inoculum delivery methods, and flood and drought conditions on root rot development of blueberry plants caused by Phytophthora cinnamomi. Results documented consistent development of root rot symptoms and reliability of a rapid disease screening protocol. This protocol can be used to evaluate chemical and biological root rot control products, to study environmental effects on root rot development, or to identify root rot tolerant blueberry germplasm. The sanitation practice of removing rosette infected primocanes of erect blackberry cultivars was evalulated to reduce fungal inoculum and rosette disease severity. Mowing treatments were applied to two rosette susceptible blackberry cultivars established in replicated plots at TCSHL in Poplarville. Blackberry plants displayed mild rosette disease symptoms in spring of 2016, and no significant differences in disease severity were found yet among treatments. Preliminary yield and quality data were collected spring 2016. In 2016, an entomology group of ARS scientists at Poplarville, MS and Wooster, OH as well as University scientists continue to develop mass-trapping and push-pull control of ambrosia beetles by placing and monitoring traps along the periphery of woodlots at different densities to intercept females before they get the chance to infiltrate nurseries and attack tree stock. In 2016, ornamental plant pathology research included installation of replicated 1.5 m deep in-ground tanks with a dual irrigation system to independently promote release of Phytophthora zoospores into containment basins and subsequent spread of infective inoculum in irrigation water on to healthy plants. Pathogen populations in containment ponds and plant disease development will be monitored weekly over the year and is just being initiated. Irrigation water treatment studies are ongoing to calculate an adjustable disinfestant dose response curve for inactivating P. nicotianae zoospores, a common pathogen of ornamental plants. As part of the greenhouse studies, protocol was developed to evaluate sanitation treatments targeted to eliminate epiphytic populations of Pseudomonas savastanoi from Loropetalum stems cuttings to propagate pathogen-free plant stock. Chemical spray trials were performed to determine the percent disease control obtained on container-grown woody ornamental shrubs based on the percent fungicide coverage obtained from different spray configurations, but the tests failed due to weather being unfavorable for disease development. However, modifications have been developed to advance the study in preparation for disease development this year. In 2016, a group of ARS and MSU entomologists conducted studies to survey pesticide (including neonicotinoids) concentrations in honey bee hives. Poplarville entomologists continue to cooperate with Utah researchers from the ARS Logan Lab to test the lethal and sublethal effects of a neonicotinoid insecticide a well as a fungicide on solitary blue orchard bees caged with treated host plants (canola). Also tested was contamination of mud and material used by the bees to partition their brood nest cells by neonicotinoid and fungicidal runoff and its effect on female nest provisioning behavior and brood survival. In addition, artificial bee nest sites were established in Austin and Kerrville, TX to entice female blueberry orchard bees to nest in cardboard tubes. Health of the brood is being assessed in Texas before testing the bee in Mississippi on commercial blueberry plantings. The bees were abundant on an early season floral host, agarita, and alternative nest sites were identified at the Zilker Botanical Garden (Austin, TX). ARS entomologists at Poplarville and Tucson showed that honey bee brood production was reduced when bees were fed sub-lethal doses (5-20 ppm) of the certain classes of insecticides called neonicotinoids. In particular, higher doses (100 ppm) reduced honey bee lifespan by a couple of days, with less food consumed and consequently less honey stored. When neonicotinoids are consumed by honey bees in tainted food, the research profiled where the insecticide is located within the hive including wax, honey, and stored pollen. ARS entomologists at Poplarville and Stoneville continue to determine the effects of combinations of neonicotinoids and other pesticides on synergist effects on honey bees as well as effects on detoxification mechanisms. Invited presentations were made on this subject at the American Honey Producers Annual meeting in Albuquerque, NM in winter 2015. In collaborations with University partners through cooperative research agreements, ARS entomologists at Poplarville identified and quantified common row crop pesticides in honey bee hives. Researchers found higher amounts of fungicides and foliar applied neonicotinoids in areas of high production agriculture than low production agriculture. Concluded when properly applied, neonicotinoid seed treatments do not pose a significant threat to honey bee health when nectar or pollen is consumed. Invited presentations were made on this subject at the American Honey Producers Annual meeting in Albuquerque, NM in winter 2015.

Accomplishments
1. A new manageable pollinator for the southeastern United States. Procuring strong commercial colonies of honey bees for crop pollination is becoming increasingly difficult and expected to detrimentally affect sustainable U.S. food production, unless alternative pollinators become available. ARS entomologists in Poplarville, Mississippi, Stoneville, Mississippi and Logan, Utah surveyed and tracked the spread of an accidentally introduced bee from Asia. The bee, commonly known as the giant resin bee, visits many exotic trees growing in the southeastern U.S. where this bee uses dilapidated wooden structures for nesting. In addition, giant resin bees readily nested in cardboard bee nesting tubes intended for gathering broods of blue orchard bees. Their field behaviors support inclusion of this bee species on a growing list of manageable native bee crop pollinators, which includes orchard bees, alfalfa leafcutting bees, alkali bees, and bumble bees.

In response to stakeholder needs, in fall 2015 the Thad Cochran Southern Horticultural Laboratory hosted an inaugural honey bee workshop. Over 70 local beekeepers were given a tour of new honey bee related research projects and shown new laboratory space including a honey extraction faculty. The highlight was their ability to obtain hands-on training about management and control of Varroa mites and small-hive beetles using actual honey bee hives.

Review Publications
Sampson, B.J., Pounders Jr, C.T., Werle, C.T., Mallette, T., Larsen, D., Chatelain, L.M., Lee, K.C. 2016. Physical interaction between floral specialist bees Ptilothrix bombiformis (Cresson) (Hymenoptera: Apidae) enhances pollination of hibiscus (section Trionum: Malvaceae). Journal of Pollination Ecology. 18(2):7-12.
Copes, W.E., Yang, X., and Hong, C.X. Phytophthora species recovered from irrigation reservoirs in Mississippi and Alabama nurseries and pathogenicity of three new species. Plant Disease 99:1390-1395.
Zhang, H., Richardson, P.A., Belayneh, B.E., Ristvey, A., Lea-Cox, J., Copes, W.E., Moorman, G. W., and Hong, C. 2016. Recycling irrigation reservoir stratification and implications for crop health and production. Journal of the American Water Resources Association 1-12. DOI: 10-1111/1752-1688.12411. 2016.
Mullen, E.R., Rutschman, P., Pegram, N., Adamczyk Jr, J.J., Patt, J.M., Johanson, E. 2016. Laser system for identification, tracking, and control of flying insects. Optics Express. 24(11):11828. doi:10.1364/OE.24.011828.